Creating Table View in ViewDidAppear - iphone

Question

I am creating a Table View in viewDidAppear, because my app requires it to be created here for multiple reasons. However I notice that I get a memory leak when I analyze my application.
I thought using the instance variable _tableView is not a good idea in any other method besides init and dealloc. Should I just use autorelease, I want to make sure the table gets released at the appropriate time.
There is a property for my Table View.
#property (nonatomic, retain) UITableView *tableView;
And I create the Table View as such:
- (void)viewDidAppear:(BOOL)animated
{
self.tableView = [[UITableView alloc]
initWithFrame:CGRectMake(0, 0, 320, 300)
style:UITableViewStyleGrouped];
// Table View properties
self.tableView.dataSource = self;
self.tableView.delegate = self;
[self.view addSubview:self.tableView];
}
- (void)viewDidDisappear:(BOOL)animated
{
self.tableView = nil;
}
- (void)dealloc
{
[_tableView release];
}

Answer 1

self.tableView is a retain property, so your synthesized setter increases the retain count. But when you create a new UITableView using alloc/init, you also increase the retain count. So this line results in tableView being retained twice:
self.tableView = [[UITableView alloc]
initWithFrame:CGRectMake(0, 0, 320, 300)
style:UITableViewStyleGrouped];
Once when you use alloc/init, and once when you call the synthesized setter using self.tableView =.
You do not have two corresponding release calls.
The proper way of handling this would be to autorelease the alloc/init'd UITableView object that you set self.tableView to, like so:
self.tableView = [[[UITableView alloc]
initWithFrame:CGRectMake(0, 0, 320, 300)
style:UITableViewStyleGrouped]
autorelease];
The rest of your code will work as expected.
As an aside, you probably don't want to create your UITableView in viewDidAppear. By that time your view has already appeared (hence the name), and you likely wanted your UITableView before that. You also probably don't want the CPU expense of creating a new UITableView every time the view appears. You probably want to create a UITableView in viewDidLoad and then reuse it, unless there is a really good reason not to.

Answer 2

Autorelease. You get one retain for the alloc and another for the property assignment (assuming it's a retained property).
Your dealloc should handle one and an autorelease the other.

Answer 3

Setting property is good, i set the property for instance variable when you want to use that variable in another class, otherwise it is not necessary ,
Since you are creating in viewDidAppear it will create always when the view appears for that controller so better relesase the tableview in ViewDidDisappear method.
If you use autorelease we wont get when it will be released so some times accessing tableview will cause crash of application,

Answer 4

On top of what the other guys have said, I'd discourage you from doing alloc in viewDidAppear because that method can be called multiple times depending upon what else goes on (and, by the way, cause leaks unless you start checking for the existence of a tableView before alloc'ing another). Doing it in viewDidLoad seems to be much safer.
As an aside, I believe that your viewDidAppear, viewDidDisappear and dealloc should all be calling their super versions, too.